Silver halide emulsions for use in silver halide photographic light-sensitive materials are, in general, chemically sensitized by using various chemical substances to obtain, for example, desired sensitivity and gradation. As typical methods for the chemical sensitization, various sensitizing methods, such as sulfur sensitization, selenium sensitization, tellurium sensitization; noble metal sensitization using, for example, gold; and combinations of these sensitizing methods, are known. Various improvements in the aforementioned sensitizing methods have been recently made to cope with a strong need, for example, for excellent granularity, high sharpness, and high sensitivity of silver halide photographic light-sensitive materials, and further rapid processing promoted by accelerating development.
Although there is a case in which a selenium sensitizer has a greater sensitizing effect than a sulfur sensitizer used in the fields of the art, such a sensitizer largely tends to cause much fogging, to result softened gradation, and to cause increased variation of sensitivity during storage. Many patent publications have been disclosed aiming to improve these drawbacks. However, satisfactory results have not yet been brought by these improvements, and there has been a strong need for basic improvement; in particular, for greater suppression of the occurrence of fogging. Also, if sulfur sensitization, selenium sensitization, or tellurium sensitization is used in combination with gold sensitization, respectively, sensitivity is significantly increased in each case. However, fogging is increased at the same time. Although, particularly, gold-selenium sensitization and gold-tellurium sensitization result in greater sensitivity than gold-sulfur sensitization, they also largely apt to result in much fogging, increased gradation softness, and increased variation in sensitivity during storage. There remains, therefore, a strong need for development of a chemical sensitization method that gives increased sensitivity, less fogging, increased gradation hardness, and less variation in sensitivity during storage.
In this situation, chalcogen compounds having a specific structure are known to act as a chemical sensitizer. For example, specific examples of a selenocarboxylic acid (Se-ester) compound are disclosed in JP-A-7-140579 (“JP-A” means unexamined published Japanese patent application), and specific examples of a cyclic selenium compound containing a nitrogen atom are disclosed in JP-A-6-317867 and JP-A-10-186563. It is also disclosed that, if these compounds are used, fogging can be suppressed to a lower level, and a rise in sensitivity can be accomplished. However, these compounds described in the above publications also have not reached a satisfactory stage, and therefore, compounds that can suppress fogging to a lower level and attain higher sensitivity have been desired.
It is also known that many selenium compounds and tellurium compounds generally have lower stability than corresponding sulfur compounds. Not a few selenium compounds and tellurium compounds to be used as chemical sensitizers have less comparative stability. When these compounds are stored in a solution state, they resultantly gradually decompose. There is, therefore, a tendency for there to be a large difference in sensitivity, fogging, gradation, and the like, between the case of producing a light-sensitive emulsion just after a solution of a selenium compound or a tellurium compound is prepared, and the case of producing a light-sensitive emulsion a while after the solution is prepared. Therefore, chemical sensitizers that suppress fogging to attain high sensitivity are desired to have higher stability.
In this situation, there has been a strong need for development of sensitizing technologies of silver halide emulsions using a chalcogen sensitizer that attain a higher rise in sensitivity; that lower occurrence of fogging; that give a contrasty image, and that are superior in storage stability and production aptitude.